Television device



Oct. 28, 1941.

U. KNICK ETAL TELEVISION DEVICE Filed March 25, 1938 @54 7 MM? W Patented Oct. 28, 1941 v UNITED STATES PATENT v OFFICE Ulrich Knick, Berlinan angenwalter, Germany, assignors tiengesellschaft,

many

Stegjlitz, and Hans-Wolfe Finkenkrug, near Berlin,

to the firm of Fernseh Ak- Zehlendorf, near Berlin, Ger- 3 Claims.

1 {The invention relates to television transmitters into jelectrical impulses, whereby the picture may be; transmitted, comprises a cathode-ray tube containing a mosaic of light-sensitive elements In Germany March 27, 1 .37

soapos itioned that it may be scanned by the cathode-ray. The mosaic is also so positioned th ftian optical image of the picture to be transrnitted, may be. formed thereon. [It has been, found that the low efliciency of such tubes depends on the low voltage available for drawing away the photo-electrons. This voltagejis. equal to the difference between the potentialoi the mosaic elements-produced by the scanning ray and the anode potential and. is usually in. theorder of volts. This means that the f osaic elements can be charged to 5 volts at the mostbby exposure to light. If it would be possible to increase the charge voltage the tube would have a higher sensibility.

one of the main objects of the invention isto improve the sensitivity of a cathode-ray tube of the abovefmentioned type.

It is a further object to produce tential difference between the mosaic elements and the; anode of the tube) A further-object is r to provide a tube or structure using two cathode rays, scanning the same mosaic plate simultaneously but at different parts thereof.

According to the invention each mosaic element is scanned first by a sharply iocussed cathode ray and is subsequently scanned a second time by another cathode ray and brought to a strongly negative potential against the anode by the second ray. Each mosaic element is then charged positively by photoelectric emission during exposure to light, so that the high potential difference is efiective during practically the whole picture scanning period.

The first cathode ray changes the potential of the elements in positive sense and the second ray in a negative sense.

The tube for carrying out this method contains besides the electron gun for the ordinary sharply focussed ray a second electron gun producing another cathode ray following the trace of the first cathode ray with a constant distance of a few lines. The speed of the electrons of the first ray is so chosen, that the impinging electrons release more secondary electrons than primary electrons are reaching the mosaic electrode. The second ray releases a number ofsecondary electrons which is smaller than the numa higher poher of the, electrons impinging on the elements.

The invention is illustratedby way of example in the accompanying drawing in which the figure shows a tube for carrying out the method of the invention. g y

The tube l contains'a, mosaic electrode 2 consisting of a signal plate, an insulating layer upon the plateand mosaic elements on the insulating layer. -A lens 3 is provided for throwing an image of-theobject onto the mosaic. trons are drawn away by the anodein form of a ringshaped metallic layer 4 arranged on the wall of the tube. An electron gun 5 is situated in an extension of the tube. I. The cathode ray is moved by deflecting systems 6 across the mosaic electrode 2 in a manner conventional in television transmissions to produce image signal currents.

The cathode 5 has a potential of -1509 volts against anode 4. The potential of anode 4 corresponds essentially to the equilibrium potential of the mosaic elements.

According to the invention the tube l contains a. second electron gun 1., The ray produced by this system is deflected, by deflecting plates 8 across the mosaic 2 in such a manner, that it follows the scanning ray in, cophase but with a constant distance of a few lines.. Cathode. I is. only slightly negative against-anode 4, so that the electrons impinge upon the mosaic elements with low velocity and produce a number of secondary electrons smaller than the number of primary electrons. The potential of the elements is therefore made more negative by the ray emitted by cathode I. is the same for all elements because they have practically the potential produced by the ray from cathode 5. The electrons coming from cathode 1 have no effect on the output becausea constant D. C. component is produced thereby. The low potential of the mosaic elements has the consequence that the electric field of the anode is much stronger and that a larger photoelectric charge is produced than in the usual cathode ray transmitters. The deflecting systems 6 and8 are fed from the same saw-tooth. It is possible to use a very small deflecting amplitude in system 8 on account of the low velocity of the ray from cathode I. This ray does not need to be as sharply focussed as the ray produced by the electron gun 5 since it is simply a potential equalizing ray for the mosaic 2 Whereas the definition of the image The photoe1ec-,

The change of potential.

elements. The trace of the returning ray is preferably displaced for the width of e. g. 5 lines backwardly in order not to disturb the scanning process. The ray may be controlled to full intensity during the return-period, so that the desired potential is imparted to the mosaic element in spite of the high scanning speed of the ray. If e. g. the anode withdrawing the electrons from the mosaic has a potential of +1000 volts it is brought to a potential of only 950 volts during the return-period. The mosaic elements acquire therefore a potential of approximately 950 volts shortly after the scanning and are charged positively by photoelectric emission from this potential on. The scanning ray touching the mosaic elements again imparts then a potential of 1000 volts producing thereby the image signal; It is preferable to dei'ocus the ray during the .a secondary emissive charge storage screen, an

anode adjacent said screen, means including said anode for generating an electron beam in said container at a velocity sumcient to cause greaterthan-unity secondary emission from said screen,

means for scanning said charge storage screen periodically with said electron beam, means also including said anode for generating another electron beam but at a velocity normally insuflicient t0 cause greater-than-unity secondary emission return stroke e. g. by changing the voltage of the focussing electron.

The invention has been described in connection with a mosaic plate carrying insulated mosaic elements. It can be used in the same manner in connection with mosaic on a semi-conductor and in connection with a pure insulating surface as carrier for the electrical charges.

It will be understood that various modifications may be made in our invention, and we desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and set forth in the appended claims.

We claim as our invention:

1. In a picture transmitting system, a cathoderay tube comprising an evacuated container, a mosaic of light-sensitive elements therein, a signal plate, an anode common to all elements, said elements being mounted adjacent to said plate whereby they are capacitively connected thereto, means for generating an electron beam in said container, means for scanning said mosaic periodically with said electron beam, means for accelerating said beam to an electron velocity sumcient to release more secondary electrons from said mosaic than primary electrons in the beam, means for generating a second electron beam, means for accelerating said second beam to such an electron velocity that less secondary electrons are released from said mosaic than primary elecfrom said screen, means for casting an optical image on said screen, and means for causing said second mentioned beam to closely follow said first mentioned beam in the scanning of-said screen.

3. In combination, an electron discharge device having elements including an anode and a mosaic of light-sensitive elements, means for producing within said device a first and a second cathode ray, said second named ray having a lower electron velocity than said first named ray, means for focusing an optical image on said mosaic to charge said light-sensitive elements individually to small positive potentials with respect to said anode, means for periodically lowering for an instant the positive potential on each light-sensitive element to produce image signal currents, said means including means for producing a scanning movement of said first named ray over said mosaic, and means for periodically lowering yet further for an instant the potential of each light-sensitive element at an interval of time closely following that at which the potential of a respective light-sensitive element was lowered by said first named ray, said last named means including means for producing a scanning movement of said second named ray in synchronized relation with said first named ray over said mosaic.

ULRICH KNICK. HANS-WOLFGANG LANGENWALTER. 

